I've heard you need to add an o-ring to the outdrives to keep the dogbones in too. Probably at both ends.
As for putting parts on backwards, we've all done it.
I was showing off my Xray XT8 build a long while ago, and some genius pointed out I had the rear hubs on backwards. It happens with some parts that can be placed either way. My personal favorite is when someone asks why their front and rear wheels turn in opposite directions and the car tries to dig itself a hole on the spot (this is caused by putting one of the diffferentials in the wrong way round, which oddly, most kits will allow you to do
).